Preservation and protection of cultural heritage artefacts by gamma irradiation in Croatia – gamma radiation treatment of common fungi on selected cultural heritage objects

Cultural heritage (CH) objects of organic origin are susceptible to degradation due to activity of various biological agents. The gamma irradiation method has already proved to be non-destructive and very effective method in saving CH objects. A CH object should be considered as a complex system with a lot of interfaces. Therefore, in the process of its protection, the interdisciplinary approach is necessary where, besides microbiological analysis, the impact of irradiation on the CH object components must be studied. Depending on radiation sensitivity of fungi 2 - 10 kGy is needed for fungal decontamination but lower dose can ensure satisfactory reduction of bioburden. However, for CH objects consisting of sensitive natural polymers, such as paper, textile and leather, it is crucial to apply the minimal dose which is still effective against biodeteriorating agents but does not affect the physical and chemical properties of the object. In this work the paper was used as the model system. The samples were inoculated with particular fungal species including primary (Aspergillus and Penicillium species), secondary (Cladosporium and Alternaria species) as well as tertiary colonizers (Fusarium species). After the irradiation at the Radiation Chemistry and Dosimetry Laboratory of the Ruđer Bošković Institute, plate count method was applied to determine the number of viable fungi and proper irradiation doses and dose rates that eliminate fungi, respectively. Impact of gamma irradiation on physico-chemical properties of the paper was performed by colorimetry and FTIR. This work will present a systematic overview of the required minimal doses for radiation treatment of the most common and specific microorganisms found on paper as based material of CH artefacts.